Learn English – “A member of” vs. “a member at”

If you look up member in almost any dictionary, all of their usage examples use member of something or another.

If you run a search of member of vs member at in Google's Ngram viewer, you will find that standard writing prefers member of; there are effectively no instances of member at in the corpus.

So you would say, "I am a member of the Riverside Tennis Club." You might use at to clarify, "I am a member of the Riverside Tennis Club at their Granite Bay location."